The invention is directed to a rotational positioning means for a magnetic disc storage and, in particular, to a positioner for a magnetic disc storage including magnetic heads carried on a swivel member movable via a drive system and including a latch for blocking movement of the swivel member in an idle position.
Positioning means fashioned as rotational positioners have prevailed in magnetic disc storages, particularly given 51/4 and 31/2 stores. Rotational positioners have a swivelling part that is seated rotationally movable on a positioning axis arranged parallel to the axis of a disc pack. This swivelling part comprises a plurality of swivel arms carrying magnetic heads and comprises carrier arms lying roughly opposite these swivel arms with respect to the positioning axis. These carrier arms carry either a coil that is deflected relative to stationary permanent magnets or a magnet, whereby the excited magnetic coil is then rigidly arranged. In the former instance, the rotational positioner is referred to as a swivel coil positioner; in the latter, it is referred to as magnetic armature positioner. The two types of rotational positioner are inherently equivalent. Leaving the structural differences out of consideration, the coil in combination with the permanent magnet or magnets shall be referred to below as a magnetic drive system of the rotational positioner.
Such rotational positioners are known, for example, from IEEE Transactions on Magnetics, Vol. MAG-17, No. 4, July 1981, pages 1392 ff or from Electronics, 21 April 1982, pages 181 ff. During ongoing operation, the magnetic heads, gliding on an air cushion, fly over the surface of the storage disc in non-contacting fashion. This air cushion collapses given downward transgression of a minimum relative speed between magnetic head and storage disc, so that the head lands on the disc surface. Such a landing dare not occur in the data region of the magnetic discs. A landing region that corresponds to an idle position of the rotational positioner is therefore usually defined on the magnetic storage disc. It is assured that the rotational positioner can be swivelled out of the idle position into the data region only when the disc storage drive is running.
In known rotational positioners, a latch means that only releases the rotational positioner after the disc storage drive has been activated is therefore provided. The latch means frequently has an enable magnet that allows a rotational motion of the swivel part only in the excited condition. In order to enable the rotational motion of the rotational positioner, the enable magnet is excited during the entire operating time of the magnetic disc storage, so that its armature remains attracted. The enable magnet must therefore be designed for continuous operation; at the same time, it represents an additional electromagnetic noise source during the operation of the magnetic disc storage.
In order to avoid these disadvantages, U.S. Pat. No. 4,710,834 discloses a positioner means for a magnetic disc storage comprising a latch means that has a latch magnetic instead of an enable magnet. The latch magnet is fashioned such in combination with a retaining spring that, following brief excitation, it mechanically holds itself and then releases the swivel part. The mechanical locking of the magnetic armature releases only when the swivel part itself swivels back into the idle position, so that the released magnetic armature blocks the swivel part. The dimensioning of the latch magnet is less critical in this solution since it is only briefly excited for the release of the swivel part. In the normal operating condition of the magnetic disc storage, moreover, the latch magnet carries no current and therefore does not form an electromagnetic noise source for the operation of the magnetic disc storage.
What the described latch mechanisms for rotational positioners nonetheless have in common is that, namely, a magnetic element that is at least briefly excited is provided in order to prevent rotational movement of the swivel part in the idle condition of the magnetic disc storage. Of necessity, however, a rotational positioner together with its latch mechanism is always arranged in the interior of the magnetic disc storage. The demand must therefore also be made of the latch mechanism that its condition satisfies clean room conditions at the time it is integrated and that, over and above this, it produces no dirt particles that could contaminate the interior of the magnetic disc storage insofar as possible during operation. Switched magnets having such operating properties and in the required, cleaned condition, however, are correspondingly expensive. It is nonetheless not assured that they always meet these demands.
U.S. Pat. No. 4,562,500 also discloses a latch means for a rotational positioner that requires no latch or enable magnet. Included in this latch means is a latch spring that is fixed laterally projecting at the swivel part of the rotational positioner and that points in the direction of the movement of the swivel piece when conducted out of the latched position. This movement, however, is opposed by a latch stop that is rotatably seated parallel to the axis of the rotational position and comprises a catch nose as well as a seating surface for the latch spring that proceeds at a right angle relative to the catch nose. The latch stop is under the pre-stress of a tension spring and thus prevents the rotational positioner from unintentionally running out of the latched position. The swivel part, however, releases itself. As soon as the drive of the rotational positioner is excited, the free end of the swivel part presses the latch spring against the catch nose and turns the catch stop while overcoming the opposing force of the tension spring. With the back edge of the seating surface, the catch stop thereby bends the catch spring and ultimately presses it out of the catch nose. The swivel part is thus freely movable as long as it does not return into the idle position.
It is advantageous in this known solution that no enable or, respectively, latch magnet is required. The type of release, however, is particularly disadvantageous. The swivel part itself thereby releases itself by a rotational motion in the direction of the operating position forced by the drive. If a reliable latching is to be guaranteed, a comprise must thus be found between the retaining force exerted by the tension spring and the release force. Relatively high frictional forces that occur at the points of friction between latch spring and latch stop, particularly at the free end of the latch spring, nonetheless continue to be unavoidable. This situation can lead to increased abrasion that forms an additional risk of contamination in the interior of the magnetic disc storage.